1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof. Note that in this specification, a semiconductor device refers to a semiconductor element itself or a device including a semiconductor element. As such a semiconductor element, a thin film transistor is given, for example. In addition, a liquid crystal display device and the like are included in the category of a semiconductor device.
2. Description of the Related Art
In recent years, semiconductor devices are indispensable to human life. A semiconductor element such as a thin film transistor included in a semiconductor device is manufactured in such a manner that a thin film is formed over a substrate and the thin film is processed into a desired shape by a photolithography method or the like. Such a manufacturing method is used for forming a liquid crystal display device (for example, a liquid crystal television). It is important for simplification of a process to reduce the number of masks used for a photolithography method. Therefore, many techniques for reducing the number of masks in a manufacturing process have been developed (for example, Patent Document 1).